In some applications of linear voltage regulators it is a requirement to detect an open load condition on the voltage output of the regulator. The open load condition is defined as a condition where the output current is less than a predetermined minimum current. The output current can be measured by including a current sense resistor in the regulator's output path. However, since the minimum output current defined as corresponding to an open load condition is usually much smaller than a typical or maximum load current, the voltage drop across the current sense resistor must be very small, and detection of the open load condition is either not accurate or requires the use of high precision comparators.
A possible approach is to place a current sense resistor in a separate current sense path connected across the regulator's power transistor. The current sense path would include a replication of the power transistor. In such a configuration, the current sense resistor can be dimensioned irrespective of the maximum output current of the regulator so as to provide a much larger voltage drop at the minimum output current defined as the open load current. This approach, however, is still not satisfactory because the overall accuracy is affected by a possible mismatch between the thresholds of the power transistor and its replication.